Satellite communications systems can emit non-ionizing radio frequency radiation (RFR) in the microwave region of the electromagnetic spectrum at intensities large enough to pose health hazards to exposed personnel. The type and severity of the potential health hazards are dependent on the emitted frequency and the intensity of the radiation, as well as the exposure time and the part(s) of the body exposed. The recognized mechanisms for adverse microwave health effects fall into the categories of thermal and non-thermal hazards. Thermal related hazards of RFR include: tissue burns, cataracts, testicular damage, and malignancies. The mechanisms and effects of low level (non-thermal) microwave RFR are not well known and remain controversial.
The microwave radiation emanating from a satellite earth station antenna in communication with a satellite or other earth station is very directional, that is, the energy is focused in a narrow beam. The intensity of the energy decreases rapidly as it travels away from the antenna. Even given this attenuation, levels exceeding the IEEE C95.1 standard maximum permissible exposure limits can exist several feet away from the antenna, and localized areas of increased intensity, called hotspots, having the potential to burn or shock can result due to the wave phenomenon called scattering.
Communication systems emitting microwave RFR at levels unsafe for human contact are in need of a device to guard personnel against these potential health hazards. Such a device is especially needed for mobile systems utilizing concealed antennas (e.g., briefcase lid mounted antennas) where, in the absence of a conspicuous antenna, bystanders may not be aware of the potential radiation hazard. The device should be one which surveys the hazard area and sets off an alarm if personnel enter this area. The device should also shut down the transmitter during an extended intrusion, but not during a momentary intrusion that may be caused, for example, by a bird quickly flying through the hazard area.
There are many known devices which detect the presence of intruders in a particular area and sound an alarm. For example, U.S. Pat. No. 5,164,706 to Chen discloses an alarm device for a briefcase or handbag. The device is attached to the briefcase by a strap. If someone approaches the briefcase and passes too near, sensors in the device detect a presence and cause an alarm to sound, deterring theft of the briefcase. U.S. Pat. No. 5,126,719 to DeSorbo discloses an alarm system for a briefcase or other item that is motion activated, causing an alarm to sound if the item containing the device is moved. The system can be remotely armed or disarmed by using a handheld transmitter/controller. U.S. Pat. No. 4,222,119 to Brunner-Schwer discloses an ultrasonic alarm that is hidden within an ordinary portable radio.
U.S. Pat. No. 4,658,385 to Tsuji discloses an obstacle detection system for mobile robots that uses ultrasonic transducers to detect and locate objects that may be obstacles for the robot, so that the robot can avoid the obstacles.
U.S. Pat. No. 4,604,735 to Parsons discloses an ultrasonic motion detection system for a faucet. Ultrasonic transducers are used to detect a person's hands below the faucet. A microprocessor circuit then opens a valve, automatically dispensing water from the faucet.
U.S. Pat. No. 4,570,247 to Walker et al. discloses an ultrasonic motion detector for use in intrusion alarms. Dual band ultrasonic transducers are used, and an alarm sounds only after motion is detected in both bands for more than a predetermined period. U.S. Pat. No. 4,263,665 to Watts also discloses an ultrasonic intrusion alarm system. The Watts system includes both sound and light alarms.
U.S. Pat. No. 4,528,563 to Takeuchi discloses a rearward obstruction sensing system for automobiles. Sensors on the automobile detect obstacles within warning zones proximate to the automobile, and sound an alarm when such an obstacle is detected. U.S. Pat. No. 4,442,512 to Kodera et al. also discloses an obstruction sensing system for automobiles, the system using ultrasonic transducers. U.S. Pat. No. 4,028,662 to Young discloses a device for automobiles which senses the presence of a car in an adjacent lane that is driving in the blind spot of the driver of the equipped automobile.
U.S. Pat. No. 4,035,798 to Hackett discloses an ultrasonic intrusion detection system that is designed to differentiate between moving targets and ambient noises that would cause false alarms. U.S. Pat. No. 3,662,371 to Lee et al. also discloses an ultrasonic intrusion detection system that differentiates between intrusions intended to cause alarm and those that should be ignored.
U.S. Pat. No. 3,879,719 to Buckley et al. discloses an intruder detection device. The device uses a UHF transmitter and an antenna producing a flat beam of radiated energy. This beam is either transmitted parallel to the ground covering the area under surveillance, or is transmitted perpendicular to the ground at the periphery of the area under surveillance. If the beam is broken by an intruder, the change in received energy at a UHF receiver causes an alarm to set off.
U.S. Pat. No. Re. 30,719 to Mills discloses an automatic sliding doorway safety device that uses acoustic wave transmitters and receivers to detect persons or objects near the doorway. The detection of a person or object near the doorway will cause the door to open automatically. If the door is already open and is in the process of closing, the detection of a person or object near the doorway will cause the door to remain open, avoiding injury to the person or object due to the closing door. U.S. Pat. No. 4,779,240 to Dorr discloses a similar doorway safety system for automatic swinging doors. This system distinguishes items that are normally near the doorway, such as railings, from persons in the doorway.
None of the listed references discloses a system which operates within a RFR hazardous region and warns an intruder of the danger of being in the region, warns a site operator of an intruder, or shuts down the transmitter in order to protect the intruder. Further, none of these systems are designed to match antenna patterns of hazardous emitting devices.